Eh, RSS is a much more efficient slag eliminator. In my opinion, RSS is waaay funner to use than DBB. Normally, I would strongly recommend getting an RSS, but there might be potential changes to it that would totally ruin its potential to quickly eliminate single targets. So I would wait until the coast is clear before thinking about getting an RSS. With Med DMG (which is the setup you have), it might take around 8-10 hits from a DBB to kill a slag in a four-man party. Once you've mastered the RSS mechanics, you can easily eliminate a slag in a matter of 3 or less hits, and you have the potential to one-shot slags. So the few places where DBB might outclass RSS is if you leave all the slags alone on d25 till the end or the place in d26 where you hit all the switches to unleash zombies. However, DBB is more player-friendly for taking out trojans, and you can consider taking DBB to FSC if trojans are giving you a bad time. If you're feeling really brave, you can even use a DBB to take on Vanaduke himself solo (although RSS does more damage if you know how to use it right).

I got a DBB just for use in FSC, but nowadays I never bring it there. To ultimately answer your question, getting DBB just for use in FSC isn't worth it. However, if you plan to do things other than FSC, DBB really shines in places like wolver dens, fiend levels, and gremlin levels. I regularly do Gauntlet runs, and DBB is great for pretty much the entire mission (disregarding the last room of the arena).

Also, a bit off topic, but I have a few suggestions regarding your loadout. If you reeeeally don't want to get an RSS for an effective slag killer, consider getting an Electron Vortex or Graviton Vortex. Electron Vortex is the more effective of the two on slags, as it does elemental damage and the shock holds them in place. Just be prepared to do a lot of PvP for the Electron Vortex. Or get overpriced recipes for Graviton (as it is not available in Hall of Heroes). Since you have a brandish as your secondary weapon, it combos beautifully with a vortex. Plant a vortex where a lot of slags are/will be, charge up your brandish, and then unleash it on the gathered crowd for massive damage. :D

Finally, if you'd like to do bombing runs sometimes with an experienced bomber, or have any more questions, feel free to send me a friend request in game. :)

Happy bombing!
~ Lizzi

DBB does work against trojans - the fuse time's just right for you to lure it to turn around, putting its back to the bomb. Against slag walkers, you're better off using RSS, Nitro or Voltaic Tempest (when there's a lot of them).

For Vanaduke, using DBB is a risky in phase 5 - you'd have to walk too close for comfort, unless you have teammates to take out the slag guards fast/shiver.

I'm gonna get RSS for FSC if the changes aren't bad

They are. It's going to become pure piercing, for one thing, but I suppose you could pick up the elemental variant.

you can't really compare RSS to DBB. One is better suited for single targets, the other has a wide radius, good speed, and no knockback.

Personally I think it's a GREAT idea to bring dbb to vana, you can even use it on the boss himself without worrying about the surrouding fireballs blocking your attacks. However, blitz has more dps against single targets, and I tend to favor electron vortex for my primary bomb there.

Have you actually tried doing this? I have. Half the time Vana just dashes away before the bomb detonates. The other half the explosion does maybe the damage of one sword-swing so you'll be in it for the long haul.

I've used Nitro to Kill Vanaduke. I don't take DBB because personally, if I'm using one of those bombs, it's because I'm solo, and I like the knockback. If I don't need the knockback, I use RSS. I pretty much never go into FSC without RSS. On a couple runs, my teammate used shiver on Vana and I used Nitro. I also did a duo bomber run without shiver, and between Qwote's RSS and my Nitro, we took him down. Yes, Vana runs. But you should be circling around Vana so he doesn't dash as much. Then you get the nitro to hit him, from the same radius as your shivermist.

I think I'd say DBB is an awesome bomb that you should get if you have any intentions at all of being a damage bomber. It makes Beast levels pure easy. And really rocks gremlins too since it knocks them down all the time. But in FSC? I think there are better bomb choices, namely the current RSS (though we don't know if that will stay).